This application is based upon and claims benefit of priority of Japanese Patent Applications No. Hei-11-17448 filed on Jan. 26, 1999, No. Hei-11-73981 filed on Mar. 18, 1999, and No. Hei-11-143764 filed on May 24, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a stereoscopic, or three dimensional, display device using a display panel such as a liquid crystal display panel.
2. Description of Related Art
A stereoscopic display device in which images having respective parallax for left and right eyes are displayed on a panel and shown to a viewer through a parallax barrier or a lenticular plate is known hitherto. In this device, however, image resolution is low because the images are shown through the parallax barrier or the lenticular plate. In addition, image brightness is decreased in the case the parallax barrier is used, while an image focus is blurred due to lens abberation in the case the lenticular plate is used.
To cope with these problems, another type of stereoscopic image display device that displays alternately respective images for left and right eyes has been proposed and used. An example of this type of display device, viewed from its top, is shown in FIG. 37. A direction-time-shared light source 1 is constituted by a convex lens 2 and a light source 3 that emits light from regions 3L and 3R alternately. An image for a left eye is projected by the light from the region 3L and an image for a right eye is projected by the light from the region 3R through a liquid crystal panel 4. Both images are alternately switched from one to the other by switching the light emitting regions 3L and 3R. Thus, stereoscopic images are shown to a viewer. However, the images displayed on the liquid crystal panel 4 have to be switched from an image for the left eye to another image for the right eye, or vice versa, in synchronism with switching of the time-shared light source. Because the images are displayed by sequentially scanning the panel, both images for the left and right eyes are simultaneously shown when the images are switched. This phenomenon is called xe2x80x9ccross-talk.xe2x80x9d
FIG. 38 is a drawing to explain the cross-talk phenomenon. To show stereoscopic images to a viewer, it is necessary to display respective images including parallax for the left and right eyes. It is ideal if the left eye image xe2x80x9cAxe2x80x9d is completely switched to the right eye image xe2x80x9cBxe2x80x9d with a switching frequency of, e.g., 60 Hz, as shown in the middle part of FIG. 38. In actual operation, however, the images displayed by sequential scanning in the vertical direction cannot be switched instantaneously. As shown in the bottom part of FIG. 38, at the beginning of left eye image display, an image xe2x80x9cA1xe2x80x9d for the right eye still remains displayed on the panel. As image data input for the left eye proceeds, the image is gradually rewritten to the image for the left eye, as shown by xe2x80x9cA2xe2x80x9d and xe2x80x9cA3.xe2x80x9d When the input for the left eye image is completed, the display is completely rewritten to the left eye image as shown by xe2x80x9cB1.xe2x80x9d At this moment, image data input for the right eye starts, and then, the right eye image is gradually written as shown by xe2x80x9cB2xe2x80x9d and xe2x80x9cB3.xe2x80x9d Since both images for the left and right eyes are displayed with a frequency of 30 Hz in the example shown in FIG. 38, the image for each eye being switched with a frequency of 60 Hz. As understood from the above, the left eye image mixed with the right eye image is actually shown to the left eye, and similarly, the right eye image mixed with the left eye image is shown to the right eye. This phenomenon is called cross-talk.
To cope with the cross-talk problem, JP-A-9-51552 proposes a display device which shows a black image at a time of switching images from one eye to the other eye. However, showing the black image between the images for both eyes causes another problem. That is xe2x80x9cflickerxe2x80x9d which is detrimental to display quality. It would be necessary to increase the display frequency to 240 Hz or higher to eliminate flicker. If the display frequency is 240 Hz, a period of time for writing one frame is 4.17 ms. Assuming the number of scanning electrodes is 480, a period of time available for writing one line is only 8.7 microseconds. The number of scanning electrodes has to be larger than 480 to display a high resolution image, making the writing period further shorter. This means that the liquid crystal used in the panel must have such characteristics that one line can be written within 8.7 microseconds or less, and the response time is 4.17 ms or less. However, a liquid crystal having such a high performance is unknown at present.
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved stereoscopic image display device in which cross-talk is suppressed without causing flicker.
A stereoscopic image display device is composed of a flat display panel, driver circuits for driving the display panel and an eye shutter to be worn by a viewer. An left eye image and a right eye image are alternately shown on the display panel, and the eye shutter is alternately switched from the left eye to the right eye, or vice versa, in response to display of the respective left and right eye images. Thereby, the displayed image is recognized as a stereoscopic image by a viewer wearing the eye shutter.
The display panel includes a number of scanning electrodes to which scanning voltages are supplied, a number of data electrodes, running perpendicularly to the scanning electrodes, to which image data are supplied, and liquid crystal such as antiferroelectric liquid crystal filling an enclosed space between the scanning and data electrodes. Pixels are formed at each intersection of both electrodes together with the liquid crystal, thereby forming a pixel matrix for displaying picture images thereon. The driver circuits supply driving voltages consisting of the scanning voltages and data voltages to the display panel in a controlled manner. The eye shutter having a left eye shutter and a right eye shutter is worn by a viewer.
The display panel is divided into a lower part and an upper part, both parts are separately and simultaneously scanned in opposite directions to write images on the pixels on the respective scanning electrodes. This scanning is called dual scanning. For example, the lower part is scanned from the center of the panel toward the lower edge of the panel, while the upper part is scanned from the center of the panel toward the upper edge of the panel in synchronism with the scanning of the lower panel. The left eye image is displayed in the first field in which all the scanning electrodes in both parts are scanned, and the right eye image is displayed in the second field following the first field. The first and second fields constitute one frame of the displayed image. The image is written on the pixels in a selecting period, held in a holding period and eliminated in an eliminating period.
Each scanning electrode is sequentially scanned one by one with a shift time, or a time interval xcex94t, from the center of the panel toward both edges of the panel. The left eye image is written in the first field, and the right eye image is written in the second field, starting at a time after a certain period has lapsed from completion of the left eye image display. For example, the image on the first scanning electrode in the second field begins to be displayed at a time when Lxcex94t(L greater than 1) has passed after the image display on the last scanning electrode in the first field started. Alternatively, a same image such as a white image for both eyes is displayed on the scanning electrodes to be scanned at the end of each field. By employing the dual scanning and properly setting the display timing, the cross-talk images appear only in narrow regions at the vicinity of both edges of the display panel.
Further, timing for switching the eye shutter from one eye to the other is properly set to suppress the cross-talk images. For example, both the left and right eye shutters are closed until the images displayed on the last scanning electrodes scanned at the end of each field are eliminated. Alternatively, only one eye shutter is open and the other eye shutter is closed until a time immediately before the image for the other eye begins to be written. For example, only the left eye shutter is open until a time immediately before the right eye image begins to be written. In combination of proper display timing and eye shutter timing, the cross-talk is further suppressed.
A certain number of scanning electrodes, e.g., a pair of scanning electrodes may be simultaneously scanned to decrease the time required to display one field of image and to increase a frame frequency. It is also possible to feed an image data, from an outside circuit, for showing a same image for both eyes on the scanning electrodes to be scanned at the end of each field.
The eye shutter may be structured so that its polarization axis automatically accords with a polarization axis of the image display panel, irrespective of its wearing angle relative to the horizontal line. A pair of round plates, each carrying a respective left and right eye shutter made of a liquid crystal panel, are rotatably mounted on an eye shutter plate. A weight is fixed on each round plate so that the round plate automatically rotates by gravity imposed on the weight, thereby placing the polarization axis to accord with the polarization axis of the display panel.
This invention may be applied also to a display panel in which single scanning is performed in place of the dual scanning. In the case of single scanning, the cross-talk images appear only on a limited number of scanning electrodes which are last scanned in each field. The voltage supplied to the scanning electrodes in the holding period may be lowered to decrease image brightness in the holding period, so that the cross-talk images are suppressed. Alternatively or in addition to decreasing the holding voltage, the image held in the holding period may be eliminated earlier to suppress the cross-talk images.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.